Distributor adjusting mechanism

ABSTRACT

Mechanism for adjusting the location of the stationary contact of the breaker points of a distributor in accordance with engine speed during operation of the engine, either automatically in response to speed or throttle opening, or manually by a remote operation from the driver&#39;&#39;s seat in an automobile.

{ 1 Dec. 4, 1973 DISTRIBUTOR ADJUSTING MECHANISM [75] Inventor: Duane A.I-lunt, East Lansing, Mich.

[73] Assignee: Donnell R. Matthews, Jr., East Lansing, Mich.

[22] Filed: May 10, 1972 [21] Appl. No.: 252,311

[52] US. Cl. 123/117 R, 123/146.5 A [51] Int. Cl. F02p 5/06 [58] Fieldof Search 123/117 R, 146.5 A, 123/149 D; 200/30 A, 30 AA, 31 R, 31 A[56] References Cited UNITED STATES PATENTS 2,020,078 11/1935Nowasielski 123/149 D 2,042,616 6/1936 McCollum 123/117 R 1,698,0891/1929 Furgason.... 123/117 R 1,336,350 4/1920 Gorman 200/31 A 1,466,8299/ 1923 Hawkins 123/ 146.5 A

1,861,417 5/1932 Klaiber 123/117 R 3,237,619 3/1966 Kind et a1.l23/l46.5 A 2,752,437 6/1956 Purdy 123/149 D OTHER PUBLICATIONSChevrolet Truck Service Manual-General Motors Corp., 1969. (pages 6Y-25thru 6Y-27.) See FIG. 4i and 9i.

Primary ExaminerLaurence M. Goodridge Assistant Examiner-Cort FlintAttorneyDonald P. Bush [5 7] ABSTRACT 10 Claims, 6 Drawing FiguresPATENTEDHEL 4mm 3 776 206 SHEET 20? 2 DISTRIBUTOR ADJUSTING MECHANISMBRIEF SUMMARY OF THE INVENTION Internal combustion engines having sparkignition are provided with a distributor which includes electricalcontacts opened and closed in timed relation to engine speed. Theignition system includes a transformer in which the high voltagesecondary is connected to the spark plugs, and the primary of thetransformer includes the breaker points. When the breaker points areclosed a circuit builds up in the primary and when the breaker pointsopen the field of the primary windings collapses, inducing a highvoltage in the secondary which produces a spark at the spark plug.

In conventional distributors in use today a cam rotor is providedusually having lobes equal to the number of cylinders or a fraction ofthe number of cylinders. One of the breaker points is adjustably mountedon a plate which is in turn angularly about adjustable the axis ofrotation of the cam, in order to effect automatic timing of the sparkwith reference to the position of the piston in each cylinder of theengine. A further adjustment of the so-called fixed contact isaccomplished by mounting it and the movable contact carried by themovable breaker arm on a sub-plate movable generally radially of thecam. The movable breaker arm is provided with a projection which isengaged by the high points or lobes of the cam which move the breakerarm in a direction to separate the contacts or breaker points aspreviously mentioned..The moveable breaker arm is spring biased so thatits contact normally engages the stationary contact except when'movedaway by operation of the cam.

From the foregoing it will be apparent that if the subplate carryingboth breaker points is moved far engough awayfrom the cam, the cam willnot engage the projection on the movable breaker arm and the contactswill remain closed. On the other hand, if the subplate is adjusted toofar in a direction toward the cam, the projection on the movable breakerarm will engage the cam at all times and the breaker points will neverclose. When the sub-plate is adjusted into an intermediate position thelobes on the cam will have the effect of opening the breaker pointsduring each passage of a lobe past the projection on the breaker arm,and the interval during which the breaker points are separated and theinterval during which the breaker points are closed is determined by theadjustment of the subplate.

It has been found by experiment that most efiicient ignition at anyparticular engine speed occurs when the sub-plate is adjusted to aposition dependent on engine speed. In general terms, at high speed thesub-plate should be adjusted away from the cam so as to reduce themaximum space between the contacts when the breaker points areseparated. However, when this adjustment is in effect engine operationis less efficient at lower speeds as for example 30-40 miles per hour.Similarly, if the stationary breaker contact is adjusted by adjustmentof the sub-plate so that the optimum gap exists for low speed operation,engine operation is less efficient at high speed.

The foregoing is of particular importance since the inefficient engineoperation, attributable to less than an optimum spark at the spark plug,causes faulty combustion and results in undesirable emissions in theengine exhaust.

By providing for an adjustment of the stationary breaker point with acorresponding adjustment of the relative duration of open and closedconditions of the breaker points, maximum engine efficiency and fuelcombustion occurs at all speeds.

In general terms, means are provided for effecting adjustment of thesub-plate carrying the stationary contact together with the movablecontact of the breaker points, either manually, from the driverscompartment while the engine is running, or automatically in directresponse to engine speed, or automatically in response to throttleposition, which in turn affects engine speed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic viewillustrating the distributor and mechanism for adjusting the sub-platecarrying the stationary and movable breaker points.

FIG. 2 is a fragmentary elevational view looking in the direction ofthearrows 22, FIG. 1.

FIG. 3 is a sectional view on the: line 33, FIG. 1.

FIG. 4 is an enlarged sectional view on the line 4-4, FIG. 1.

FIG. 5 illustrates a centrifugal device for operating the adjustablemeans in accordance with engine speed.

FIG. 6 is a fragmentary perspective diagrammatic view illustratingmanually controlled mechanism for effecting the adjustment.

DETAILED DESCRIPTION Referring first to FIG. 1 there is shown adistributor 10 with the cover removed, the distributor including arotatable cam 12 illustrated as of generally hexagonal shape and adaptedto be rotated on its axis in accordance with engine speed. Within thehousing of the distributor is a plate 14 which is angularly adjustableabout the axis of the cam 12, such adjustment normally being effected bymeans responsive to manifold vacuum as is well understood. Rotation ofthe plate 14 and the breaker point assembly carried thereby has theeffect of advancing or retarding the spark in accordance with manifoldvacuum.

The contacts or breaker points which are connected in the primary of thetransformer comprise a stationary contact or breaker point 16, and a.movable contact or breaker point 18 carried by a movable breaker arm 20pivoted as indicated at 22 and urged in a counterclockwise direction bya spring (not shown). The spring has the effect of maintaining thecontacts 16 and 18 closed except when they are opened and retained inopen position by operation of the cam 12. The movable breaker arm 20 isprovided with a projection 24 which extends toward the cam 12 and whichis adapted to be engaged by the lobes or high points of the cam as theypass the location of the projection or cam follower 24.

The stationary contact 16 and the movable breaker arm 20 carrying themovable contact 18 are mounted on an adjustable sub-plate 26 movable ona bracket 28 about the axis of the pivot 22. The bracket 28 is providedwith an upstanding ear 30 carrying an adjusting screw 32 which isthreaded through an opening in an car 34 on the sub-plate 26 and ismounted for rotation only in the ear 30. A compression spring 35cooperates with the head 35a of the screw to provide for positioning ofthe sub-plate 26 as a consequence of rotation of the screw 32.(Accordingly, rotation of the screw adjusts the sub-plate 26 in adirection such that the projection 24 of the breaker arm 20 movesgenerally radially toward and away from the axis of the cam 12, thestationary contact 16 of course partaking of such adjustment.)

The foregoing adjustment is normally provided in distributors so thatthe maximum operational gap between the contacts 16 and 18 may beadjusted, while the engine is not running. Such adjustment is necessaryto .maintain a predetermined maximum gap when the surfaces of thebreaker points are dressed to remove pits or the like after extendeduse.

In accordance with the present invention, means are provided whichconnect to the adjusting screw 32 so that this screw may be rotated oradjusted during operation of the engine and independently of theposition of the rotatable support plate 14 on which the remainingstructure is mounted. This means, in the embodiment of the inventionillustrated in FIGS. 1-4, comprises a torsion wire 36 shown as forming apart of a wire assembly 38 including a flexible sheath 39, the end ofthe wire extending into a suitable non-circular recess in the head 35aof the adjusting screw.

Inasmuch as the plate 14 which carries the bracket 28 and the sub-plate26 for angular adjustment about the axis of the shaft 12, is movablewith respect to the housing of the distributor, it is necessary toprovide an enlarged opening 39a through which the wire assembly 38passes to the interior of the distributor.

The means for rotating the torsion wire 36 may, as previously stated, bemanual and operated from a remote position, or it may be automatic.

As seen in FIG. 1, an automatic operation of the gap adjustment isprovided. The conventional accelerator pedal of an automatic vehicle isconnected by a link 40 to a carburetor diagrammatically indicated at 42.Mounted adjacent the link 40 for movement in a direction longitudinallythereof is a slotted plate 42 having an elongated slot indicated at 44.Adjustable longitudinally of the slot is an abutment indicated at 46which includes a screw 48 which may be loosened to permit adjustment ofthe abutment longitudinally of the slot.

Clamped to the link 40 is an abutment device 50 having a portion 52extending through the slot and carrying a nut 54 and screw 56 whichretains the two halves of the abutment assembled in the relationshipillustrated in FIG. 2. It will be observed from this FIGURE that thelocation of the abutment 46 determines the length of an elongated slotin which the abutment device 50 is longitudinally movable. Connected toone end of the plate 42 is a Bowden wire device 58 comprising theflexible wire 60 longitudinally slidable in a flexible sheath 62. Uponpredetermined movement of the accelerator link 40 the abutment device 50engages one end or the other of the portion of the slot determined bythe position of the abutment 46 and will effect a longitudinal movementof the wire 60. The other end of the wire is positioned adjacent atransmission housing 64 details of which are best seen in FIG. 3. Thesheath 62 of the Bowden wire is mounted in fixed position relative tothe housing 64 and the projecting end of the wire 60 is connectedthrough a tension spring 66 to a rod 68 which in turn connects to aspring biased rack 70 slidable in the housing 64. A dashpot device isprovided comprising a cylinder 72 in which a piston 74, connected to therod 68, is longitudinally slidable. The interior of the cylinder 72 ischarged with hydaulic fluid and the piston 74 is provided with one ormore restricted passages 76 having a check valve 78 associatedtherewith. Each check valve is provided with a small passage (not shown)permitting a restricted flow of hydraulic fluid therethrough when thevalves are in closed position. It will be observed that when a pull isexerted on the wire 60, the spring 66 is tensioned but with the checkvalve 78 in closed position, movement of the rack 70 will be retardeduntil the hydraulic fluid can flow through the restricted ports providedin the check valve 78. Accordingly, when the accelerator pedal is movedabruptly to a position corresponding to wide open throttle, which willincrease the engine speed to a maximum consistent with the engineloading, the adjustment of the distributor is delayed so that it doesnot take place until the engine speeds up in response to openingmovement of the throttle.

Longitudinal movement of the rack 70 is transmitted through a pinion 80to a gear 82 carrying an output shaft 84 at the end of which is provideda toothed clutch element 86 received in a cylindrical housing 88. Asecond cup-shaped clutch element 90 is received within the housing andthe parts are retained in assembled position by a closure 92.Accordingly, rotation of the shaft 84 is transmitted to an output shaft94 recessed as indicated at 96 for the reception of a noncircular orsquare end portion 98 of the torque transmitting wire 36.

With the foregoing construction it will be observed that when theaccelerator pedal link is moved in a direction to open the throttle(upwardly in FIG. 1),

predetermined movement of the link 40 will cause engagement between theabutment device 50 and the end of the slot 44 as determined byadjustable abutment 46. This will exert a pull on the wire 60 and, wherethe dashpot construction including the cylinder 72 is employed, willtension the spring 66. Tension in the spring 66 will urge the rackupwardly as seen in FIG. 3 at a rate determined by the escapement portsin the check valves 78, thus introducing a timed delay in adjustment ofthe breaker point gap and hence, the duration of closure period of thebreaker points to permit the engine speed to increase in response tothrottle opening. With the Bowden wire device 58 stationary and with theengine stopped, an adjustment may be. made in the position of thesub-plate 26 to provide a predetermined maximum gap between the breakerpoints, such as is required after the breaker points have been dressedso as to remove material therefrom. This is accomplished by removing orloosening the closure 92 from the housing 88 to permit the teeth of theclutch elements 86 and to be separated. Thus, with the clutch element 86stationary the shaft 94 and wire 36 may be rotated to effect therequired adjustment of the sub-plate 26, after which the closure 92 isagain threaded down to maintain the clutch elements in engagement. Itwill be understood that this adjustment is made periodically only asrequired by wear and/or pitting of the breaker points. While a lostmotion arrangement is provided by the elongated slot 44 and theadjustable abutment 46, it will be appreciated that if desired,longitudinal movement of the accelerator link 40 might be used to effecta continuous adjustment of the sub-plate 26. However, this continuousadjustment is not required and the adjustment means illustrated in FIGS.1 and 2 is satisfactory. With this arrangement the breaker points may beprovided with the maximum separation suitable for starting and low speedoperation and will retain this adjustment until the throttle opening isincreased to a predetermined amount, after which the adjustment of thebreaker points is initiated.

Referring now to FIG. 5 there is illustrated an arrangement in whichmeans responsive directly to engine speed are provided for effectingadjustment of the sub-plate 26. In this case the shaft 102 is suitablyconnected to be driven at a speed which is a direct function of enginespeed. Fixed to the shaft 102 is a ring 104 and slidably longitudinallyon the shaft 102 is a second ring 106. The rings 104 and 106 areinterconnected by links 108 which in turn are connected to centrifugalweights 110. A compression spring 112 is provided intermediate the ringsand urges the lower ring 106 downwardly as seen in FIG. 5.

Another ring 114 is provided which is longitudinally slidable on theshaft 102 but does not partake of rotation therewith. Rings 106 and 114are interconnected by bearings diagrammatically indicated at 116 and thering 114 is retained in engagement with the bearings 1 16 by compressionsprings l 18. Vertical movement of the ring 1 14 is transmitted to thewire 60 of the Bowden wire device 58 by connectors 120. It will beunderstood that the illustration of FIG. 5 is diagrammatic and thesupport for the shaft 102 and the associated centrifugal mechanism isindicated at 122.

With this mechanism, movement of the wire 60 may be continuous inaccordance with changes in engine speed. Conversely, however, the spring112 may be selected such that movement of the actuating ring 114 doesnot commence until a predetermined minimum engine speed has beenattained.

Referring now to FIG. 6 there is illustrated an ar rangement in whichthe mechanism may be manually operated by the driver of a motor vehiclefrom a position within the vehicle. In this embodiment of the inventionthe distributor is diagrammatically indicated at 130 and the torsionwire assembly 38 is shown as entering the interior of the distributorthrough an opening 132. A cable 134 is illustrated as wound around arotatable drum 136 connected to a crank 138 located within the driverscompartment, The crank 138 includes an indicating pointer 140 which maybe associated with a dial if desired. The housing 142 contains suitablegearing (not shown) for converting longitudinal movement of the cable134 to rotational movement of the torsion wire included in the wireassembly 38. It will be appreciated that the cable 134 may be connectedto a rack 142a identical with the rack 70 shown in FIG. 3, connected toatension spring 143 urging the rack in a di rection away from the cable134. Accordingly, rotation of the drum 136 may move the rack against thetension of the spring within the housing 142 and when the crank 138 ismoved in the opposite direction the spring will maintain the cable 134taut and will move the rack in the opposite direction.

In this embodiment of the invention the adjusted position of thesub-plate 26 may be indicated by indicia associated with the pointer 140or an indicator 144 may be provided. The indicator 144 is a dwellindicator which is available on the market and which will show theduration of closure of the breaker points. As the length of time whichthe breaker points are closed becomes shorter upon higher speed, thecrank 138 may be rotated in the appropriate direction to increase thelength of each period during which the breaker points are closed, Ingeneral, the pointer 146 of the dwell indicator will move in onedirection as the dwell period shortens upon an increase in speed, andcan be brought back into a desirable intermediate range by suitablerotation of the crank 138. When engine speedfalls off, the needle willmove in the opposite direction and will indicate that suitable rotationof the crank in the opposite direction is required to bring the dwellperiod back within the optimum range.

What I claim as my invention is:

1. In combination, a spark distributor for an internal combustion engineof a motor vehicle comprising a housing, a rotary cam within saidhousing, a support plate within said housing, a stationary contact onsaid plate, a movable contact on said plate movable toward and away fromsaid stationary contact, a cam follower engageable with said cam andconnected to said movable contact for moving said movable contact awayfrom engagement with said stationary contact when engaged by said cam,means within said housing for adjusting said stationary and movablecontacts as a unit in a direction to cause said cam follower to movegenerally radially of said rotary cam, and actuating means operableduring operation of said vehicle for operating said adjustment means, inwhich said actuating means comprises means responsive to engine speedfor effecting an adjustment which is a function of engine speed.

2. The combination defined in claim 1 in which said speed responsivemeans comprises a centrifugally operated speed responsive deviceconnected to the engine.

3. The combination defined in claim 1 in which said speed responsivemeans comprises means connected to the throttle positioning mechanism ofthe engine.

4. In combination, a spark distributor for an internal combustion engineof a motor vehicle comprising a housing, a rotary cam within said!housing, a support plate within said housing, a stationary contact onsaid plate, a movable contact on said plate movable toward and away fromsaid stationary contact, a cam follower engageable with said cam andconnected to said movable contact for moving said movable contact awayfrom engagement with said stationary contact when engaged by said cam,means within said housing for adjusting said stationary and movablecontacts as a unit in a direction to cause said cam follower to movegenerally radially of said rotary cam, and actuatingmeans operableduring operation of said vehicle for operating said adjustment means, inwhich said contacts are mounted on a sub-plate movable on said supportplate, an arm pivoted to said sub-plate on which said movable contact iamounted, said arm having cam-engaging means positioned in the path of acam portion when the contacts are closed, and means mounting saidsub-plate on said support plate for the aforesaid adjustment in adirection which moves said cam-engaging means generally radially of saidrotary cam, in which said actuating means comprises means responsive toengine speed for effecting an adjustment which is a function of enginespeed.

5. In combination, a spark districtor for an internal combustion engineof a motor vehicle comprising a housing, a rotary cam within saidhousing, a support plate within said housing, a stationary contact onsaid plate, a movable contact on said plate movable toward and away fromsaid stationary contact, a cam follower engageable with said cam andconnected to said movable contact for moving said movable contact awayfrom engagement with said stationary contact when engaged by said cam,means within said housing for adjusting said stationary and movablecontacts as a unit in a direction to cause said cam follower to movegenerally radially of said rotary cam, and actuating means operableduring operation of said vehicle for operating said adjustment means, inwhich said means within said housing for adjusting said contacts asaforesaid is rotary means and in which said actuating means comprisesmeans movable generally in a straight line, and gearing operable toconvert such motion to rotarymotion, and means for applying such rotarymotion to said rotary means.

6. In combination, a spark distributor for an internal combustion engineof a motor vehicle comprising a housing a rotary cam within saidhousing, a support plate within said housing, a stationary contact onsaid plate, a movable contact on said plate movable toward and away fromsaid stationary contact, a cam follower engageable with said cam andconnected to said movable contact for moving said movable contact awayfrom engagement with said stationary contact when engaged by said cam,means within said housing for adjusting said stationary and movablecontacts as a unit in a direction to cause said cam follower to movegenerally radially of said rotary cam, actuating means operable duringoperation of said vehicle for operating said adjustment means, andadditional means for adjusting said contacts to provide the aforesaidadjustment thereof independent of the aforesaid means for making theaforesaid adjustment, in which said additional means comprisesrelatively adjustable clutch members located in said actuating means.

7. The combination defined in claim 6 in which said first mentionedadjusting means within said housing is rotatable, and in which saidclutch members are angularly adjustable and located in said firstmentioned adjusting means.

8. In combination, a spark distributor for an internal combustion engineof a motor vehicle, comprising a rotary cam, a first support mounted forangular adjustment about the axis of rotation of said cam, a stationarycontact on said support, a movable contact on said support movable intoand out of contact with said stationary contact, a member movablycarried by said support on which said movable contact is mounted, a camfollower on said member engageable with said rotary cam, resilient meansconnected to said member urging said member in a direction to cause saidcam follower to engage said cam and said movable contact to engage saidstationary contact, whereby said movable contact is moved away from saidstationary contact as a result of engagement between said cam followerand said cam, actuating means operable during operation of said vehicleto effect an adjustment of at least one of said contacts independent ofthe adjustment resulting from angular adjustment of said first supportto effect opposite variations in the intervals during which saidcontacts remain in closed and open condition, and a second support onwhich said stationary contact and said movable member are mounted, saidsecond support being movably mounted on said first support foradjustment in a direction which moves said cam follower generallyradially of said cam, in which said actuating means comprises meansresponsive to engine speed for effecting an adjustment which is afunction of engine speed.

9. The combination defined in claim 8 in which said speed responsivemeans comprises a centrifugally operated speed responsive deviceconnected to the engine.

10. The combination defined in claim 8 in which said speed responsivemeans comprises means connected to the throttle positioning mechanism ofthe engine.

1. In combination, a spark distributor for an internal combustion engineof a motor vehicle comprising a housing, a rotary cam within saidhousing, a support plate within said housing, a stationary contact onsaid plate, a movable contact on said plate movable toward and away fromsaid stationary contact, a cam follower engageable with said cam andconnected to said movable contact for moving said movable contact awayfrom engagement with said stationary contact when engaged by said cam,means within said housing for adjusting said stationary and movablecontacts as a unit in a direction to cause said cam follower to movegenerally radially of said rotary cam, and actuating means operableduring operation of said vehicle for operating said adjustment means, inwhich said actuating means comprises means responsive to engine speedfor effecting an adjustment which is a function of engine speed.
 2. Thecombination defined in claim 1 in which said speed responsive meanscomprises a centrifugally operated speed responsive device connected tothe engine.
 3. The combination defined in claim 1 in which said speedresponsive means comprises means cOnnected to the throttle positioningmechanism of the engine.
 4. In combination, a spark distributor for aninternal combustion engine of a motor vehicle comprising a housing, arotary cam within said housing, a support plate within said housing, astationary contact on said plate, a movable contact on said platemovable toward and away from said stationary contact, a cam followerengageable with said cam and connected to said movable contact formoving said movable contact away from engagement with said stationarycontact when engaged by said cam, means within said housing foradjusting said stationary and movable contacts as a unit in a directionto cause said cam follower to move generally radially of said rotarycam, and actuating means operable during operation of said vehicle foroperating said adjustment means, in which said contacts are mounted on asub-plate movable on said support plate, an arm pivoted to saidsub-plate on which said movable contact ia mounted, said arm havingcam-engaging means positioned in the path of a cam portion when thecontacts are closed, and means mounting said sub-plate on said supportplate for the aforesaid adjustment in a direction which moves saidcam-engaging means generally radially of said rotary cam, in which saidactuating means comprises means responsive to engine speed for effectingan adjustment which is a function of engine speed.
 5. In combination, aspark districtor for an internal combustion engine of a motor vehiclecomprising a housing, a rotary cam within said housing, a support platewithin said housing, a stationary contact on said plate, a movablecontact on said plate movable toward and away from said stationarycontact, a cam follower engageable with said cam and connected to saidmovable contact for moving said movable contact away from engagementwith said stationary contact when engaged by said cam, means within saidhousing for adjusting said stationary and movable contacts as a unit ina direction to cause said cam follower to move generally radially ofsaid rotary cam, and actuating means operable during operation of saidvehicle for operating said adjustment means, in which said means withinsaid housing for adjusting said contacts as aforesaid is rotary meansand in which said actuating means comprises means movable generally in astraight line, and gearing operable to convert such motion to rotarymotion, and means for applying such rotary motion to said rotary means.6. In combination, a spark distributor for an internal combustion engineof a motor vehicle comprising a housing a rotary cam within saidhousing, a support plate within said housing, a stationary contact onsaid plate, a movable contact on said plate movable toward and away fromsaid stationary contact, a cam follower engageable with said cam andconnected to said movable contact for moving said movable contact awayfrom engagement with said stationary contact when engaged by said cam,means within said housing for adjusting said stationary and movablecontacts as a unit in a direction to cause said cam follower to movegenerally radially of said rotary cam, actuating means operable duringoperation of said vehicle for operating said adjustment means, andadditional means for adjusting said contacts to provide the aforesaidadjustment thereof independent of the aforesaid means for making theaforesaid adjustment, in which said additional means comprisesrelatively adjustable clutch members located in said actuating means. 7.The combination defined in claim 6 in which said first mentionedadjusting means within said housing is rotatable, and in which saidclutch members are angularly adjustable and located in said firstmentioned adjusting means.
 8. In combination, a spark distributor for aninternal combustion engine of a motor vehicle, comprising a rotary cam,a first support mounted for angular adjustment about the axis ofrotation of said cam, a stationary contact on said support, a movablecontact on said support movable into and out of contact with saidstationary contact, a member movably carried by said support on whichsaid movable contact is mounted, a cam follower on said memberengageable with said rotary cam, resilient means connected to saidmember urging said member in a direction to cause said cam follower toengage said cam and said movable contact to engage said stationarycontact, whereby said movable contact is moved away from said stationarycontact as a result of engagement between said cam follower and saidcam, actuating means operable during operation of said vehicle to effectan adjustment of at least one of said contacts independent of theadjustment resulting from angular adjustment of said first support toeffect opposite variations in the intervals during which said contactsremain in closed and open condition, and a second support on which saidstationary contact and said movable member are mounted, said secondsupport being movably mounted on said first support for adjustment in adirection which moves said cam follower generally radially of said cam,in which said actuating means comprises means responsive to engine speedfor effecting an adjustment which is a function of engine speed.
 9. Thecombination defined in claim 8 in which said speed responsive meanscomprises a centrifugally operated speed responsive device connected tothe engine.
 10. The combination defined in claim 8 in which said speedresponsive means comprises means connected to the throttle positioningmechanism of the engine.